1. Field of the Invention
The present invention relates to an ion implanter. More particularly, the present invention relates to an ion implanter capable of effectively reducing sputtering particles therein.
2. Description of the Related Art
Recently, 256 Megabyte DRAM cells have been fabricated by a process satisfying a design rule provided that a width between circuit lines is less than 0.18 xcexcm. However, when the 0.18 xcexcm design rule is applied in the fabrication process, peptides, which are generated in a process chamber, have a tendency to cause defects in semiconductor devices, thereby decreasing a yield of products. Particularly, when 1 Gigabyte DRAM cells or 4 Gigabyte DRAM cells, conventionally known as the next generation memory devices, are developed, the particles generated in the process chamber during fabrication of the devices cause various technical difficulties and fabrication limitations. Hence, the particles are generally recognized as a barrier to be overcome in developing the next generation memory device.
Accordingly, semiconductor device manufacturers have made a great effort and invested significant amounts of time to determine causes of the particles and methods of managing the particles in order to reduce their numbers and to prevent wafer pollution due to the particles in the fabrication of the semiconductor device.
In particular, wafer pollution caused by the particles has a particularly substantial effect on electrical characteristics of a semiconductor device when the particles are generated in an ion implanting process.
According to a conventional ion implanting process, accelerated ions are impacted to the wafer disposed in an ion implanter and then a predetermined amount of ions are implanted to a surface of the wafer at a predetermined depth.
The particles generated in the ion implanter are generally divided into two categories: mechanical particles and electrical particles. Most of the electrical particles are sputtering particles generated by high-speed impact of the ions to a metal surface and activation by an electrostatic force of an ion beam. The mechanical particles are generated by frictional heat due to motion of a rotational device or a transmission system of the ion implanter.
In the case of the mechanical particles, a cause of the particles is easily found and the damage to the wafer is minor. Accordingly, high level technology is not required to trace the mechanical particles in comparison with the electrical particles.
However, in the case of the electrical particles, the electrostatic force of the ion beam consisting of positive ions activates the minute and fine particles and renders the particles to be sputtered. Accordingly, the electrical particles cause significant damage to the wafer and high level technology is required to trace the particles.
The present invention has been made to solve the aforementioned problem. Accordingly, it is a feature of an embodiment of the present invention to provide an ion implanter capable of analyzing a cause of particles generated therein and restraining generation of the particles by changing a structure of elements of the ion implanter, resulting in a decrease of particle-induced damage of wafers processed therein.
In order to provide these and other features and advantages of the present invention, there is provided an ion implanter having means for scanning an ion beam on a wafer. The scanning means, on which the wafer is mounted, moves the wafer in a region where the ion beam is irradiated. A detecting means, which is fixedly mounted adjacent to the scanning means, detects the ion beam that is overly scanned out of the scanning means. The detecting means has an inclined surface so that a portion of the detecting means adjacent to the scanning means is positioned below a surface of the wafer that is disposed on the scanning means.
According to one embodiment of the present invention, an inclination angle of the inclined surface of the detecting means is limited to approximately 10 degrees to 30 degrees. When the inclination angle is less than 10 degrees, a gradient of the inclined surface is so small that the particles are scattered on the wafer, and thus wafer pollution is not sufficiently prevented. Similarly, when the inclination angle is more than 30 degrees, the gradient of the inclined surface is so large that the secondary electrons generated by sputtering cannot be controlled by means of a faraday cup.
The scanning means may include either a rotary disc applied in a batch type ion implanter or a wafer holder applied in a single type ion implanter. The detecting means preferably includes a spillover cup or a sampling beam cup that is mounted adjacent to the scanning means to detect the ion beam that is overly scanned out of an edge of the scanning means.